Abstract
An external cavity lasing system, which operates at 2.4 μm and involves an InGaAsSb Fabry-Pérot gain chip, was
developed and characterized. The system was set up in a Littrow configuration to achieve a tuning range of about 100
nm. Continuous, mode-hope free tuning was observed with variation of grating angle. The threshold current of the lasing
chip varied from 86 mA down to 70 mA for lasing in Fabry-Pérot (FP) and external cavity (ECL) modes, respectively. A
dependence of the threshold current on lasing wavelength was observed. The tuning range was found to depend on the
semiconductor gain profile and also on the intensity of the optical feedback through the collimation-dispersion system.
Drifting of the wavelength, as observed in intra cavity semiconductor lasers, was not observed for drive currents of up to
350 mA in regions close to the gain peak. Single mode ECL lasing could be sustained in this range at a significantly
weaker optical feedback. Traces of FP lasing were, however, observed at currents in the range of 100-200 mA for
wavelengths in the shoulder regions of the gain profile. In these cases, an increase of drive current resulted in mode
hopping to multi-mode FP lasing. Our results confirm the competing nature of FP lasing with that of ECL mode of
lasing. The onset of multi-mode FP lasing, and eventual hopping to these modes, can be correlated with the gain profile,
drive current, and optical feedback.
